The present invention relates to a method for recording information on an optical recording medium, especially a method for recording information on a write-once type optical recording medium. Also, the invention relates to an information recording apparatus for recording information on an optical recording medium, especially an information recording apparatus for recording information on a write-once type optical recording medium.
In recent years, there have been proposed next-generation optical recording media which have a much larger recording capacity in comparison to conventional ones and which allow the achievement of an extremely higher data transfer rate, and some of them have come into practical use (see Patent Document 1, JP-A-2003-203383). Unlike a conventional optical recording medium, with such next-generation optical recording media, a laser beam of a wavelength of about 205 nm and an objective having a numerical aperture of about 0.85 are used for data recording and reproduction. This allows the beam spot diameter of a laser beam to be narrowed down to about 0.39 μm in a plane of recording, thereby achieving a recording capacity of about 25 GB/side and a data transfer rate of about 36 Mbps at a reference linear velocity (about 4.9 m/sec).
Also, in regard to next-generation optical recording media, various types of optical recording media such as read-only type, write-once type, and rewritable type have been proposed like existing optical recording media including CDs (Compact Disc) and DVD (Digital Versatile Disc). However, of these media, write-once type ones have been known to have the feature that a heat amount per unit time required for data recording is increased with an increase in targeted recording linear velocity. In order to increase a heat amount per unit time, it is necessary to use a higher-power semiconductor laser, or to further lengthen the length of an ON-pulse pattern, i.e. the time to set the intensity of a laser beam at a recording-power level.
[Patent Document 1] JP-A-2003-203383
However, a laser beam to be used for next-generation optical recording media is a light in a blue-color wavelength region as described above, and a semiconductor laser capable of generating such laser beam at a high output power is very expensive. Hence, in order to increase a heat amount to be applied per unit time thereby to enable recording at an extremely high linear velocity e.g. a fourfold data rate, it is useful to lengthen the length of an ON-pulse pattern, i.e. the time to set the intensity of a laser beam at a recording-power level as far as possible. Therefore, adopting a pulse train pattern (i.e. so-called solid pattern) in which one ON-pulse pattern is used to form a record mark can make the time to set the intensity of a laser beam at a recording-power level longest. However, using such pulse train pattern poses a problem such that an unwanted heat pocket is produced in a record layer in forming a long record mark, thereby causing a thermal interference and thus deteriorating recording properties.